DJAMENA (AFP) - Around 100 bodies were found Friday in a mass grave on the outskirts of the town of Damasak after it was liberated from Boko Haram Islamists, a Chadian army spokesman told AFP.

Soldiers discovered the bodies - some decapitated - under a bridge just outside the town, which was retaken from Boko Haram on March 9 by troops from Chad and Niger.

"There are about 100 bodies spread around under the bridge just outside the town," said Colonel Azem Bermandoa Agouna, adding that he had visited the scene himself close to the border with Niger.

He claimed the massacre probably happened about two months ago and said: "This is the work of Boko Haram."

It was, however, impossible to verify the claim independently.

Colonel Bermandoa Agouna said several of the victims had been decapitated while other had been shot.

"There are heads here and bodies there, the mass grave has become like a termite mound," he added.

Chad and Niger launched a vast air and ground offensive against Boko Haram in the area on March 8, quickly taking Damasak from the Nigerian Islamist militants.

According to a Chadian army source, the militants suffered heavy losses in the push, with some 200 killed in fighting on Sunday for the loss of 10 Chadian soldiers with 20 wounded.

"Operation Mai Dounama", named after a 13th-century emperor of Borno province in northern Nigeria, aims to destroy Boko Haram bases close to Niger, a Nigerien army spokesman said Thursday.

Boko Haram took Damasak on Nov 24, killing around 50 people and forcing another 3,000 to flee, according to the UN's High Commissioner for Refugees.